Scott Bakula is doing a convincing job of throttling a Vulcan on the set of Enterprise, the latest - and arguably grittiest - Star Trek incarnation. His character, Captain Jonathan Archer, has just torn a strip off the Vulcan for forcibly "mind melding" with a reluctant female officer (also a Vulcan, and as it happens a particularly attractive example of the pointy-eared species). Fists fly, and lots of manly grunting ensues. Then the director calls "Cut!" and the two actors return to their marks for another take. And another. And three more.

The crew finally breaks for lunch close to 5pm, but Bakula's meal goes into his dressing room fridge to be warmed up later. While the others eat, he sits down to talk about his role in this prequel to the original Star Trek series.

Last May's announcement that the next captain would be played by the star of Quantum Leap, the rather groovy 90s time-travel series, surprised industry watchers and Trekkers (as fans prefer to be called) alike: handing the captain's chair to an established leading actor marked a radical departure for the series. Previous captains - including William Shatner, Avery Brooks (of Deep Space Nine), and Kate Mulgrew (of Voyager) - were little-known character players when they took on their roles. And as far as US viewers were concerned, Patrick Stewart (of The Next Generation) was just some bald English bloke they had never heard of.

So, money aside, how was the relatively well-known Bakula persuaded to don a polyester jumpsuit and bark orders such as "Straight ahead, warp factor nine!" with a straight face? "I have a production company on the Paramount lot and about a year ago, I was talking to the studio about another series [of Quantum Leap]," he says. "But they said, 'Let us ask you about this: what do you think about being the first captain on the first starship in the Star Trek prequel?' And I said, 'That sounds pretty great.' "

The new series is set 150 years into the future from the present day - a century before the other Star Trek films and TV shows. This means that the familiar Star Trek technology is very much in the prototype stage. Captain Archer's ship is forced to launch early and only goes up to warp factor five, just over half the speed of Captain Kirk's vessel, and the crew are frightened to use the transporter because the science hasn't yet been perfected. At one point the gravity stabiliser goes wobbly, and Captain Archer, who is taking a shower, ends up floating around the bathroom with the water streaming up past him.

"I don't believe that I would have done the series if it had just been the next generation of Star Trek, but this was very interesting to me," says Bakula. "We're only 150 years from today so there's the notion that this is within the realm of possibility. It's very accessible and very human. We're hands-on. We don't talk to computers, the doors don't open by themselves. We have to push buttons and move things and carry stuff. There's a very improvisational feel, and it's just made for this nice feeling of adventure and excitement, which is what true exploration is like."

After 35 years, four TV series and nine feature films, the American public could be forgiven for greeting the premiere of yet another Star Trek series with a giant collective yawn. Only it didn't. The two-hour pilot was watched by more than 12m viewers. Judging from their comments on internet fansites, Trekkers are positively giddy with delight that Enterprise has reversed a four-year Star Trek ratings slide.

The only thing they don't like is the title song, Faith of the Heart, the first Star Trek theme with lyrics added - and particularly naff ones at that. Written for the cloying film Patch Adams by Diane Warren, queen of the sickly power ballad, the original version was sung by Rod Stewart. But the rights were too expensive so it was "reinterpreted" by Russell Watson, the steelworker-turned-tenor from Salford. Appalled Star Trek fans have sent in petitions to get rid of it, and some have even protested outside Paramount Studios, but to no avail.

Bakula experienced similarly rabid devotion from fans when he was in Quantum Leap. And he knows all about those strange conventions where aficionados dress up as their favourite characters and quote lines from old scripts to the actors. They don't bother him. "Paramount imposes no obligation upon us to participate in anything outside of doing a good job here at work," he says. "I have friends who have had a great time travelling the world doing Star Trek conventions. But I've got a life full of kids and a very busy time here, so I didn't want to have to appear at five conventions a year or something like that. It's purely up to me."

At 47, Bakula is a year younger than William Shatner was in 1979 when he put on James T Kirk's uniform for the first time in 10 years for Star Trek: the Motion Picture. But unlike Shatner at that age, Bakula is not yet in need of a corset; nor does he have a sleeping Tribble glued to the top of his head. His hair is his own, and there is still plenty of it.

When it comes to temperament, the affable actor could not be more unlike the notoriously irascible Shatner, who is said not to receive many Christmas cards from the Star Trek cast and crew he used to work with. Both men, however, have recorded albums: Bakula put out a CD of songs he performed as Quantum Leap characters; and on his 1968 album Transformed Man, William Shatner famously murdered classics such as Lucy in the Sky With Diamonds and Mr Tambourine Man. The difference is that Bakula can sing. He started out in musical theatre and received a Tony award nomination for the Broadway musical Romance, Romance. (He lost the lead in Phantom of the Opera to Michael Crawford.)

On screen, he projects an easygoing warmth and likeability. He is the same in person: friendly, attentive and polite. Middle-America handsome, he is just the type of guy you would want in charge of Earth's first venture into deep-space exploration. In real life, he has a reputation as a workaholic. Since Quantum Leap ended in 1993, he has popped up regularly on the big and small screens in almost 30 different projects. He was Candice Bergen's boyfriend in the sitcom Murphy Brown, and one half of the gay couple living next door to Kevin Spacey in the film American Beauty. He also produced and starred in the recent US television movie What Girls Learn, a story of two teenage sisters coping with life in a new town and their mother's breast cancer. He cast himself as the mother's boyfriend.

Although the original Star Trek series, which began in 1966, lasted only three seasons, each of its successors ran for seven. If Enterprise follows that pattern, won't it restrict his freedom to do anything else? He shrugs. "I really don't know yet how it will affect me. My production company is still moving forward. I'll have a limited amount of time when I'll be available to do other work."

Family is his priority. The father of three sons and a daughter, aged from two to 17, he wants to be around while they grow up. Filming Enterprise in Los Angeles - when so many productions are made in Canada or on the east coast - was a major factor in his decision to do the show. "I was looking for something I could stay in town with because of my kids," he says. "I've made some great movies up there but running to Canada every few months is taxing on your home life. To be able to find a series like this - not on location, not working till dawn every Friday night and Saturday morning - there's a certain civility to the whole thing."